What is it?

There are two distinct components here: an open source Gmail API
written for the .NET framework, and a proof of concept Windows
application built on top of that API that provides basic remote Gmail
functions.

I developed these tools in the hopes of encouraging others to create
interesting Gmail services. Admittedly, this project may not have a very
long shelf life, as
Sergey has intimated possible mail forwarding and RSS support, not
to mention Gmail's recent listing of
upcoming features(Gmail login required) that estimates a
slew of features that are listed as “working on it” or “we'll try”. The
address book import is currently listed as “sometime soon” but
it's actually available now in the Contacts window. As Sergey mentioned,
an enterprise version of Gmail would be well received, and I have no
doubt that there would an API to go along with that (I recently
integrated a
Google Search Appliance, and can attest to its extensibility).
Whether or not Google is interested in pursuing such features for the
public side remains to be seen. Nonetheless, I hope to keep this project
going, and wouldn't mind joining the Gmail team — there are lots of
features I'd like to see implemented in Gmail.

About the Gmail Agent Applet

I'm sure most of you are more interested in the applet, so here are
the features:

Multiple account support

Balloon notification of new messages with message preview

Address book view and import (from tab-delimited text files)

The system requirements are:

Windows 2000, or higher

Microsoft .NET Framework v1.1

I haven't tried this with
Mono — I doubt it works, but if it does, please let me know. If you
are interested in POP access to Gmail, check out
Pop Goes
the Gmail (also a .NET project).

This is a proof of concept application, and there
are plenty of idiosyncrasies. It works great for me, but your results
may vary. I welcome anyone who wants to contribute to polishing this
app.

About the Gmail Agent API

The goal of the API is to provide an extensible foundation for
interfacing with Gmail. The objects in this namespace should be
abstracted enough to be able to be adapted to any future changes Gmail
makes.

The main workhorse of this class is
GmailAdapter. It is
responsible for communicating with Gmail and maintaining the login and
session information through the duration of the application. The
GmailSession object holds all the state information for a single Gmail
account, including a GmailThreadCollection of GmailThread objects. The
GmailContact object represents a single Gmail address book entry. Again,
GmailAdapter provides the methods to fill a GmailContact with
information from Gmail.

Connection Overview

One oddity with the API is that it uses TLS instead of SSL for the
encryption layer. For reasons unknown, the SSL provider was extremely
intermittent and often failed to establish a secure link so I manually
set the ServicePointManager
to use TLS 1.0. This seems to be a common problem among .NET developers,
and if anyone has a stable solution, I'd love to hear about it.

Here is a bare-bones example of how to establish a connection with
Gmail using the API:

About the Gmail engine and protocol

You've probably noticed that Gmail's interface is extremely
fast when compared to other web-based email systems like Yahoo!
Mail and Hotmail. This is a result of Gmail's placement of the
UI engine on the client-side as a JavaScript module. Whenever
you log in to Gmail, a copy of the UI engine is loaded into one
of the HTML page frames and remains there for the duration of
your session (credit has to be given to
Oddpost
for being the first ones who perfected this idea). Subsequent
actions from the Gmail interface are then routed through the
Gmail UI engine in your browser, which in turn makes HTTP
requests (via the
<a object? request http xml the title?using href="http://jibbering.com/2002/4/httprequest.html">XmlHttpRequest object) to the Gmail server, interprets the
DataPack (more on this later), and updates the UI dynamically.
In contrast, Hotmail and Yahoo! Mail follow traditional web
application models and reload the entire UI after almost every
action.

The item most relevant to this project is what I refer to as
the “DataPack”, a base HTML file that contains only JavaScript
array declarations that the UI engine parses and then uses to
determine what to update. The advantages of this should be
immediately obvious: reduced traffic load, and increased
functionality — especially for developers who no longer have to
resort to crude “screen scraping” techniques to interface with
web applications. Although the ideal situation for external
developers would be an XML-based DataPack, the JavaScript
version is sufficient (and I suspect it was chosen for
performance reasons as well).

The DataPack format consists of individual “DataItems”, or
JavaScript arrays wrapped in a envelope function. An example:

D(["ts",0,50,106,0,"Inbox","fd36721220",154]);

The function D()
references a runtime evaluator within the Gmail engine, which
then interprets the attached array parameters. The
"ts" element
indicates that this is a threadlist summary item, and the
subsequent elements denote start index, threads per page,
estimated total, threadlist title, threadlist timestamp, and
total threads. This is the same format that is applied to all
array parameters sent through the DataPack:

[<DataItem_name>(,<custom_attribute>)]

The mappings to all the DataItems can be found in the engine
code source (/gmail?view=page&name=js).
For instance, qu
contains quota information, while
ct contains
category (a.k.a. labels) definitions. Read through that file if
you really want to get everything you can out of Gmail.

Determining the right URL to retrieve the DataPack is pretty
straightforward, as most requests will return the same basic
information, such as quota, category count, and inbox count. The
main thing that changes is the threadlist summary, which depends
on what page you're looking at. All the main folders — inbox,
starred, trash, spam, etc. — are all really just pre-defined
searches within Gmail. For example, the inbox DataPack URL is:

/gmail?search=inbox&view=tl&start=0&init=1&zx=

The search query for all unread threads is:

/gmail?search=query&q=is%3Aunread&view=tl&start=0&init=1&zx=

The main parameters are
search= and
q=, which
define what set of threads the user is requesting. The
zx= parameter
is a proxy cache defeater, and I've omitted it here for brevity.
See GmailAdapter.MakeUniqueUrl() for more information.

Gmail exploits another advantage of the DataPack model to
increase efficiency by allowing for an empty document. This is
employed by the 2-minute auto-refresh request. The inbox URL
adds a few more parameters:

The tlt=
parameter is the thread list timestamp, which is treated like a
checksum in determining the state of the client versus the
mailbox state on the server. If the client timestamp is older
than the one on the server, then a full DataPack is sent.
Otherwise, Gmail sends an essentially empty DataPack.

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License

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